Side channel blowers or pumps are generally known and have been described in a number of applications. In a motor vehicle, they serve, for example, to convey fuel or to blow in secondary air into the exhaust gas system. The drive is normally performed by an electric motor driving the impeller. At its periphery, the impeller is substantially designed such that it forms a circumferential vortex duct together with the axially opposite conveying duct. From the part of the impeller forming the vortex, duct conveying blades extend perpendicularly towards the opposite part of the conveying duct formed in the housing so that pockets are formed between the conveying blades. When the impeller rotates, the conveyed fluid in the pockets is accelerated in the circumferential direction and in the radial direction by the conveying blades so that a circulating turbulent flow is formed in the conveying duct.
Side channel blowers have been described in which only a conveying duct in an axial side of the impeller is formed in a housing part, as well as side channel blowers in which a conveying duct is formed on both axial sides of the impeller, in which case both conveying ducts are in fluid communication with each other. With such a side channel blower, one of the conveying ducts is formed in a housing part that serves as a cover, while the other conveying duct is formed in the housing part at which the drive unit is usually fastened, the impeller being arranged on the shaft thereof at least such that it rotates therewith.
In order to obtain as good a conveyance or pressure increase as possible, it is necessary to use as large a part of the circumference of the conveying duct as possible. For this reason, the inlet and the outlet must be spaced as far as possible from each other along the circumference, as seen in the direction of rotation of the impeller, where a short-circuit flow between the inlet and the outlet must be prevented by an interruption region. Such side channel blowers have been found problematic with respect to a high noise development which is caused, in particular, by pulsations that occur due to sudden pressure pulses of the air conveyed.
These pressure pulses occur, among other instances, immediately after the sweeping of each of the conveying blades at the beginning of the interruption region since the pockets between the conveying blades still hold compressed air that has not been expelled completely through the outlet, which air is suddenly accelerated against the walls thereof when the interruption portion is reached. This results in significantly increased noise emissions.
For a reduction of these noise emissions, DE 10 2008 24 741 B4 describes a side channel blower for feeding secondary air in which a housing cover of the housing is formed with a recess upstream of the inlet, as seen in the direction of impeller rotation, the recess becoming constantly larger towards the inlet and having a width that substantially corresponds to the width of the conveying duct.
A side channel blower is also described in DE 10 2009 006 652 A1 which also comprises a housing part with a conveying duct and a housing cover with a second conveying duct formed on the side of the first conveying duct opposite the impeller. The radially limiting wall of the interruption region between the inlet and the outlet has an additional recess formed therein downstream of the outlet, as seen in the direction of impeller rotation.
Both measures may result in a significant noise reduction, however, undesirable noise emissions remain when conveying against a closed control valve, i.e., at maximum counter-pressure in the conveying chambers.